The present invention relates, in general, to driver circuits and, in particular, to modulation circuits for laser diodes.
Laser diodes are presently employed in optical radar systems, for instance, which determine the range or distance between the laser diode and an object of interest. Modulator circuits selectively turn such diodes on and off. A prior art modulator circuit employs a silicon controlled rectifier (SCR) connected with the laser diode and a capacitor. Control or trigger signals are applied to the gate of the SCR to render the SCR conductive to thereby discharge the capacitor through the laser diode to provide a transmitted light pulse.
The foregoing prior art circuit is useful for many applications wherein the rise time of the emitted light pulse is not critical. Rise time of a pulse can be defined as the time it takes for the amplitude of the pulse to go from 10% to 90% of its peak magnitude, for instance. Typically the fastest light pulse rise times for prior art SCR circuits is approximately 10 nanoseconds. Such circuits are useful for measuring ranges of from 80 to 90 feet, for instance. The accuracy of such ranging devices is proportional to the rise time of the emitted pulse of light. Laser diode radars for measuring ranges from 30 to 40 feet, however, require light pulses having approximately 3 nanosecond rise times. Prior art circuits for providing driving signals for enabling these faster rise times generally include a printed wiring board having numerous passive and active components located thereon. Such circuits are too expensive, unreliable and large for many applications requiring inexpensive, reliable, miniaturized circuitry.